This invention is in the field of maize breeding, specifically relating to an inbred maize line designated NP2222.
The goal of plant breeding is to combine in a single variety or hybrid various desirable traits. For field crops, these traits may include resistance to diseases and insects, tolerance to heat and drought, reducing the time to crop maturity, greater yield, and better agronomic quality. With mechanical harvesting of many crops, uniformity of plant characteristics such as germination and stand establishment, growth rate, maturity, and plant and ear height, is important.
Field crops are bred through techniques that take advantage of the plant""s method of pollination. A plant is self-pollinated if pollen from one flower is transferred to the same or another flower of the same plant. A plant is cross-pollinated if the pollen comes from a flower on a different plant. Plants that have been self-pollinated and selected for type for many generations become homozygous at almost all gene loci and produce a uniform population of true breeding progeny. A cross between two different homozygous lines produces a uniform population of hybrid plants that may be heterozygous for many gene loci. A cross of two plants each heterozygous at a number of gene loci will produce a population of hybrid plants that differ genetically and will not be uniform.
Maize (Zea mays L.), often referred to as corn in the United States, can be bred by both self-pollination and cross-pollination techniques. Maize has separate male and female flowers on the same plant, located on the tassel and the ear, respectively. Natural pollination occurs in maize when wind blows pollen from the tassels to the silks that protrude from the tops of the ears.
A reliable method of controlling male fertility in plants offers the opportunity for improved plant breeding. This is especially true for development of maize hybrids, which relies upon some sort of male sterility system. There are several options for controlling male fertility available to breeders, such as: manual or mechanical emasculation (or detasseling), cytoplasmic male sterility, genetic male sterility, gametocides and the like.
Hybrid maize seed is typically produced by a male sterility system incorporating manual or mechanical detasseling. Alternate strips of two maize inbreds are planted in a field, and the pollen-bearing tassels are removed from one of the inbreds (female). Providing that there is sufficient isolation from sources of foreign maize pollen, the ears of the detasseled inbred will be fertilized only from the other inbred (male) and the resulting seed is therefore hybrid and will form hybrid plants.
The laborious, and occasionally unreliable, detasseling process can be avoided by using cytoplasmic male-sterile (CMS) inbreds. Plants of a CMS inbred are male sterile as a result of factors resulting from the cytoplasmic, as opposed to the nuclear, genome. Thus, this characteristic is inherited exclusively through the female parent in maize plants, since only the female provides cytoplasm to the fertilized seed. CMS plants are fertilized with pollen from another inbred that is not male-sterile. Pollen from the second inbred may or may not contribute genes that make the hybrid plants male-fertile. Seed from detasseled fertile maize and CMS produced seed of the same hybrid can be blended to insure that adequate pollen loads are available for fertilization when the hybrid plants are grown.
There are several methods of conferring genetic male sterility available, such as multiple mutant genes at separate locations within the genome that confer male sterility, as disclosed in U.S. Pat. Nos. 4,654,465 and 4,727,219 and chromosomal translocations as described in U.S. Pat. Nos. 3,861,709 and 3,710,511, the disclosures of which are specifically incorporated herein by reference. There are many other methods of conferring genetic male sterility in the art, each with its own benefits and drawbacks. These methods use a variety of approaches such as delivering into the plant a gene encoding a cytotoxic substance associated with a male tissue specific promoter or an antisense system in which a gene critical to fertility is identified and an antisense to that gene is inserted in the plant (EPO 89/3010153.8 and WO 90/08828).
Another system useful in controlling male sterility makes use of gametocides. Gametocides are not a genetic system, but rather a topical application of chemicals. These chemicals affect cells that are critical to male fertility. The application of these chemicals affects fertility in the plants only for the growing season in which the gametocide is applied (see Carlson, Glenn R., U.S. Pat. No. 4,936,904, which is incorporated herein by reference). Application of the gametocide, timing of the application and genotype specificity often limit the usefulness of the approach.
The use of male sterile inbreds is but one factor in the production of maize hybrids. The development of maize hybrids requires, in general, the development of homozygous inbred lines, the crossing of these lines, and the evaluation of the crosses. Pedigree breeding and recurrent selection breeding methods are used to develop inbred lines from breeding populations. Breeding programs combine the genetic backgrounds from two or more inbred lines or various other germplasm sources into breeding pools from which new inbred lines are developed by selfing and selection of desired phenotypes. The new inbreds are crossed with other inbred lines and the hybrids from these crosses are evaluated to determine which of those have commercial potential. Plant breeding and hybrid development are expensive and time-consuming processes.
Pedigree breeding starts with the crossing of two genotypes, each of which may have one or more desirable characteristics that is lacking in the other or which complements the other. If the two original parents do not provide all the desired characteristics, other sources can be included in the breeding population. In the pedigree method, superior plants are selfed and selected in successive generations. In the succeeding generations the heterozygous condition gives way to homogeneous lines as a result of self-pollination and selection. Typically in the pedigree method of breeding five or more generations of selfing and selection is practiced: F1 to F2; F3 to F4; F4 to F5, etc.
Recurrent selection breeding, backcrossing for example, can be used to improve populations of either self or cross-pollinating crops. Backcrossing can be used to transfer a specific desirable trait from one inbred or source to an inbred that lacks the trait. This can be accomplished, for example, by first a superior inbred (recurrent parent) to a donor inbred (non-recurrent parent), that carries the appropriate gene(s) for the trait in question. The progeny of this cross is then mated back to the superior recurrent parent followed by selection in the resultant progeny for the desired trait to be transferred from the non-recurrent parent. After five or more backcross generations with selection for the desired trait, the progeny will be homozygous for loci controlling the characteristic being transferred, but will be like the superior parent for essentially all other genes. The last backcross generation is, then selfed to give pure breeding progeny for the gene(s) being transferred. A hybrid developed from inbreds containing the transferred gene(s) is essentially the same as a hybrid developed form the same inbreds without the transferred genes. As the varieties developed using recurrent selection breeding contain almost all of the characteristics of the recurrent parent, selecting a superior recurrent parent is desirable.
A single cross maize hybrid results from the cross of two inbred lines, each of which has a genotype that complements the genotype of the other. The hybrid progeny of the first generation is designated F1. In the development of commercial hybrids only the F1 hybrid plants are sought. Preferred F1 l hybrids are more vigorous than their inbred parents. This hybrid vigor, or heterosis, can be manifested in many polygenic traits, including increased vegetative growth and increased yield.
The development of a maize hybrid involves three steps: (1) the selection of plants from various germplasm pools for initial breeding crosses; (2) the selfing of the selected plants from the breeding crosses for several generations to produce a series of inbred lines, which, although different from each other, breed true and are highly uniform; and (3) crossing the selected inbred lines with different inbred lines to produce the hybrid progeny (F1). During the inbreeding process in maize, the vigor of the lines decreases. Vigor is restored when two different inbred lines are crossed to produce the hybrid progeny (F1). An important consequence of the homozygosity and homogeneity of the inbred lines is that the hybrid between a defined pair of inbreds will always be the same. Once the inbreds that give a superior hybrid have been identified, the hybrid seed can be reproduced indefinitely as long as the homogeneity of the inbred parents is maintained.
A single cross hybrid is produced when two inbred lines are crossed to produce the F1 progeny. A double cross hybrid is produced from four inbred lines crossed in pairs (Axc3x97B and Cxc3x97D) and then the two F1 hybrids are crossed again (Axc3x97B)xc3x97(Cxc3x97D). Much of the hybrid vigor exhibited by F1 hybrids is lost in the next generation (F2). Consequently, seed from hybrids is not used for planting stock.
Hybrid seed production requires elimination or inactivation of pollen produced by the female parent. Incomplete removal or inactivation of the pollen provides the potential for self-pollination. This inadvertently self-pollinated seed may be unintentionally harvested and packaged with hybrid seed. Once the seed is planted, it is possible to identify and select these self-pollinated plants. These self-pollinated plants will be genetically equivalent to the female inbred line used to produce the hybrid. Typically these self-pollinated plants can be identified and selected due to their decreased vigor. Female selfs are identified by their less vigorous appearance for vegetative and/or reproductive characteristics, including shorter plant height, small ear size, ear and kernel shape, cob color, or other characteristics.
Identification of these self-pollinated lines can also be accomplished through molecular marker analyses. See, xe2x80x9cThe Identification of Female Selfs in Hybrid Maize: A Comparison Using Electrophoresis and Morphologyxe2x80x9d, Smith, J. S. C. and Wych, R. D., Seed Science and Technology 14, pp. 1-8 (1995), the disclosure of which is expressly incorporated herein by reference. Through these technologies, the homozygosity of the self-pollinated line can be verified by analyzing allelic composition at various loci along the genome. Those methods allow for rapid identification of the invention disclosed herein. See also, xe2x80x9cIdentification of Atypical Plants in Hybrid Maize Seed by Postcontrol and Electrophoresisxe2x80x9d Sarca, V. et al., Probleme de Genetica Teoritca si Aplicata Vol. 20 (1) p. 29-42.
As is readily apparent to one skilled in the art, the foregoing describes only two of the various ways by which the inbred can be obtained by those looking to use the germplasm. Other means are available, and the above examples are illustrative only.
Maize is an important and valuable field crop. Thus, a continuing goal of plant breeders is to develop high-yielding maize hybrids that are agronomically sound based on stable inbred lines. The reasons for this goal are obvious: to maximize the amount of grain produced with the inputs used and minimize susceptibility of the crop to pests and environmental stresses. To accomplish this goal, the maize breeder must select and develop superior inbred parental lines for producing hybrids. This requires identification and selection of genetically unique individuals that occur in a segregating population. The segregating population is the result of a combination of crossover events plus the independent assortment of specific combinations of alleles at many gene loci that results in specific genotypes. The probability of selecting any one individual with a specific genotype from a breeding cross is infinitesimal due to the large number of segregating genes and the unlimited recombinations of these genes, some of which may be closely linked. However, the genetic variation among individual progeny of a breeding cross allows for the identification of rare and valuable new genotypes. These new genotypes are neither predictable nor incremental in value, but rather the result of manifested genetic variation combined with selection methods, environments and the actions of the breeder. Thus, even if the entire genotypes of the parents of the breeding cross were characterized and a desired genotype known, only a few, if any, individuals having the desired genotype may be found in a large segregating F2 population. Typically, however, neither the genotypes of the breeding cross parents nor the desired genotype to be selected is known in any detail. In addition, it is not known how the desired genotype would react with the environment. This genotype by environment interaction is an important, yet unpredictable, factor in plant breeding. A breeder of ordinary skill in the art cannot predict the genotype, how that genotype will interact with various climatic conditions or the resulting phenotypes of the developing lines, except perhaps in a very broad and general fashion. A breeder of ordinary skill in the art would also be unable to recreate the same line twice from the very same original parents, as the breeder is unable to direct how the genomes combine or how they will interact with the environmental conditions. This unpredictability results in the expenditure of large amounts of research resources in the development of a superior new maize inbred line.
According to the invention, there is provided a novel inbred maize line, designated NP2222. This invention thus relates to the seeds of inbred maize line NP2222, to the plants of inbred maize line NP2222, and to methods for producing a maize plant by crossing the inbred line NP2222 with itself or another maize line. This invention further relates to hybrid maize seeds and plants produced by crossing the inbred line NP2222 with another maize line. The invention further relates to methods for producing maize lines derived from inbred maize line NP2222 and from hybrid maize lines developed therefrom, and to maize lines derived by use of those methods.
The invention is also directed to inbred maize line NP2222 into which one or more specific, single gene traits, for example transgenes, have been introgressed from another maize line. Preferably, the resulting line has essentially all of the morphological and physiological characteristics of inbred maize line of NP2222, in addition to the one or more specific, single gene traits introgressed into the inbred, preferably the resulting line has all of the morphological and physiological characteristics of inbred maize line of NP2222, in addition to the one or more specific, single gene traits introgressed into the inbred. The invention also relates to seeds of an inbred maize line NP2222 into which one or more specific, single gene traits have been introgressed and to plants of an inbred maize line NP2222 into which one or more specific, single gene traits have been introgressed. The invention further relates to methods for producing a maize plant by crossing plants of an inbred maize line NP2222 into which one or more specific, single gene traits have been introgressed with themselves or with another maize line. The invention also further relates to hybrid maize seeds and plants produced by crossing plants of an inbred maize line NP2222 into which one or more specific, single gene traits have been introgressed with another maize line. The invention is also directed to a method of producing inbreds comprising planting a collection of hybrid seed, growing plants from the collection, identifying inbreds among the hybrid plants, selecting the inbred plants and controlling their pollination to preserve their homozygosity.
Inbred maize lines are typically developed for use in the production of hybrid maize lines. Inbred maize lines need to be highly homogeneous, homozygous and reproducible to be useful as parents of commercial hybrids. There are many analytical methods available to determine the homozygotic and phenotypic stability of these inbred lines.
The oldest and most traditional method of analysis is the observation of phenotypic traits. The data is usually collected in field experiments over the life of the maize plants to be examined. Phenotypic characteristics most often observed are for traits associated with plant morphology, ear and kernel morphology, insect and disease resistance, maturity, and yield.
In addition to phenotypic observations, the genotype of a plant can also be examined. There are many laboratory-based techniques available for the analysis, comparison and characterization of plant genotype; among these are Isozyme Electrophoresis, Restriction Fragment Length Polymorphisms (RFLPs), Randomly Amplified Polymorphic DNAs (RAPDs), Arbitrarily Primed Polymerase Chain Reaction (AP-PCR), DNA Amplification Fingerprinting (DAF), Sequence Characterized Amplified Regions (SCARs), Amplified Fragment Length Polymorphisms (AFLPs), and Simple Sequence Repeats (SSRs) which are also referred to as Microsatellites.
Some of the most widely used of these laboratory techniques are Isozyme Electrophoresis and RFLPs as discussed in Lee, M., xe2x80x9cInbred Lines of Maize and Their Molecular Markers,xe2x80x9d The Maize Handbook, (Springer-Verlag, New York, Inc. 1994, at 423-432). Isozyme Electrophoresis is a useful tool in determining genetic composition, although it has relatively low number of available markers and the low number of allelic variants among maize inbreds. RFLPs have the advantage of revealing an exceptionally high degree of allelic variation in maize and the number of available markers is almost limitless. Maize RFLP linkage maps have been rapidly constructed and widely implemented in genetic studies. One such study is described in Boppenmaier, et al., xe2x80x9cComparisons among strains of inbreds for RFLPsxe2x80x9d, Maize Genetics Cooperative Newsletter, 65:1991, pg. 90. This study used 101 RFLP markers to analyze the patterns of 2 to 3 different deposits each of five different inbred lines. The inbred lines had been selfed from 9 to 12 times before being adopted into 2 to 3 different breeding programs. It was results from these 2 to 3 different breeding programs that supplied the different deposits for analysis. These five lines were maintained in the separate breeding programs by selfing or sibbing and rogueing off-type plants for an additional one to eight generations. After the RFLP analysis was completed, it was determined the five lines showed 0-2% residual heterozygosity. Although this was a relatively small study, it can be seen using RFLPs that the lines had been highly homozygous prior to the separate strain maintenance.
The production of hybrid maize lines typically comprises planting in pollinating proximity seeds of, for example, inbred maize line NP2222 and of a different inbred parent maize plant, cultivating the seeds of inbred maize line NP2222 and of said different inbred parent maize plant into plants that bear flowers, emasculating the male flowers of inbred maize line NP2222 or the male flowers of said different inbred parent maize plant to produce an emasculated maize plant, allowing cross-pollination to occur between inbred maize line NP2222 and said different inbred parent maize plant and harvesting seeds produced on said emasculated maize plant. The harvested seed are grown to produce hybrid maize plants.
Inbred maize line NP2222 can be crossed to inbred maize lines of various heterotic group (see e.g. Hallauer et al. (1988) in Corn and Corn Improvement, Sprague et al, eds, chapter 8, pages 463-564) for the production of hybrid maize lines.
All linear measurements are in centimeters unless otherwise noted.
In interpreting the foregoing color designations, reference may be made to the Munsell Glossy Book of Color, a standard color reference. Color codes: 1. light green, 2. medium green, 3. dark green, 4. very dark green, 5. green-yellow, 6. pale yellow, 7. yellow, 8. yellow-orange, 9. salmon, 10. pink-orange, 11. pink 12. light red, 13. cherry red, 14. red, 15. red and white, 16. pale purple, 17. purple, 18. colorless, 19. white, 20, white capped, 21. buff, 22. tan, 23. brown, 24. bronze, 25. variegated, 26. other. Heat Units per day were calculated using the standard formula:
HU={MaxTemp (86)+Min Temp (50)]/2-50.
NP2222 differs from A632 for several different traits. These traits are:
NP2222 is an earlier maturity inbred than A632. The heat unit accumulation to all of the flowering stages is less for NP2222 than A632. The heat units to 10% Pollen Shed is 1213 for NP2222 and is 1280 for A632. Heat units to 50% Pollen Shed is 1240 for NP2222 as compared to 1311 for A632. Heat units to 50% Silk Emergence is 1248 for NP2222 and 1360 for A632.
The days to 50% silk emergence is also significantly different for NP2222 than A632. NP2222 reaches 50% silk emergence in 67 days maturity as compared to 72 days for A632.
NP2222 has a significantly lower ear placement than A632. The ear height of NP2222 is 72 cm. The ear height of A632 is 93 cm.
The Length of the Top Ear Internode is significantly longer on NP2222 at 16 cm as compared to 14 on A632.
The NP2222 leaf color is lighter than the A632 leaf. The NP2222 leaf is a medium green (02 or 5GY 4/4) and the A632 leaf is dark green (03 or 5GY 3/4).
The Leaf Sheath Pubescence on NP2222 is rated a 2 and is significantly different than A632 rated a 6.
Some of the most distinct differences of NP2222 and A632 occur in the tassel. The most pronounced of these differences is the Tassel Branch Angle. The Tassel Branch Angle of NP2222 is 17 degrees while the branch angle for A632 is 44 degrees. NP2222 has a very upright tassel branch angle. The tassel length of NP2222 is also significantly longer than A632. The NP2222 Tassel is 47 cm long while the A632 Tassel is 35 cm.
The tassels of these two inbreds also differ in coloration. The anther color of the two inbreds is significantly different. The NP2222 anther color is green-yellow (05 or 2.5GY 8/6). The A632 anther color is green yellow with pale purple shading. The glume color of NP2222 is green-yellow (05 or 2.5GY 8/6) with purple shading. The glume color of A632 is green-yellow (05 or 5GY 5/6) with the purple coloration (only) on the glume margins. The glume color bars of A632 have a slight purple shade. The glume color bars of NP2222 are light green to green-yellow.
Another pronounced color difference of these two inbreds is the color of the silk. The silk color of NP2222 is green-yellow (05 or 2.5GY 8/6) with purple shaded ends. The purple shaded ends of NP2222 are 17 or 5RP 3/8. The A632 silk is green-yellow (05 or 2.5GY 8/6).
The ear of NP2222 is different than the ear of A632. The Ear Diameter of NP2222 is 40 cm while the ear of A632 is 37 cm. The Ear Weight of NP2222 is 128 gm as compared to 78 gm of A632. The Cob diameter of NP2222 is significantly smaller at 21 mm than A632 at 23 mm. NP2222 has 4 percent Round Kernels on the ear as compared to 23 percent on A632. The NP2222 plant has fewer dropped ears at harvest than A632. The Dropped Ear Percentage for NP2222 is 0 while A632 is 5.
The invention also encompasses plants of inbred maize line NP2222 and parts thereof further comprising one or more specific, single gene traits which have been introgressed into inbred maize line NP2222 from another maize line. Preferably, one or more new traits are transferred to inbred maize line NP2222, or, alternatively, one or more traits of inbred maize line NP2222 are altered or substituted. The transfer (or introgression) of the trait(s) into inbred maize line NP2222 is for example achieved by recurrent selection breeding, for example by backcrossing. In this case, inbred maize line NP2222 (the recurrent parent) is first crossed to a donor inbred (the non-recurrent parent) that carries the appropriate gene(s) for the trait(s) in question. The progeny of this cross is then mated back to the recurrent parent followed by selection in the resultant progeny for the desired trait(s) to be transferred from the non-recurrent parent. After three, preferably four, more preferably five or more generations of backcrosses with the recurrent parent with selection for the desired trait(s), the progeny will be heterozygous for loci controlling the trait(s) being transferred, but will be like the recurrent parent for most or almost all other genes (see, for example, Poehlman and Sleper (1995) Breeding Field Crops, 4th Ed., 172-175; Fehr (1987) Principles of Cultivar Development, Vol. 1: Theory and Technique, 360-376).
The laboratory-based techniques described above, in particular RPLP and SSR, are routinely used in such backcrosses to identify the progenies having the highest degree of genetic identity with the recurrent parent This permits to accelerate the production of inbred maize lines having at least 90%, preferably at least 95% more preferably at least 99% genetic identity with the recurrent parent, yet more preferably genetically identical to the recurrent parent, and further comprising the trait(s) introgressed from the donor patent. Such determination of genetic identity is based on molecular markers used in the laboratory-based techniques described above. Such molecular markers are for example those known in the art and described in Boppenmajer, et al., xe2x80x9cComparisons among strains of inbreds for RFLPsxe2x80x9d, Maize Genetics Cooperative Newsletter (1991) 65, pg. 90, or those available from the University of Missouri database and the Brookhaven laboratory database. The last backcross generation is then selfed to give pure breeding progeny for the gene(s) being transferred. The resulting plants have essentially all of the morphological and physiological characteristics of inbred maize line NP2222, in addition to the single gene trait(s) transferred to the inbred. Preferably, the resulting plants have all of the morphological and physiological characteristics of inbred maize line NP2222, in addition to the single gene trait(s) transferred to the inbred. The exact backcrossing protocol will depend on the trait being altered to determine an appropriate testing protocol. Although backcrossing methods are simplified when the trait being transferred is a dominant allele, a recessive allele may also be transferred In this instance it may be necessary to introduce a test of the progeny to determine if the desired trait has been successfully transferred.
Many traits have been identified that are not regularly selected for in the development of a new inbred but that can be improved by backcrossing techniques or genetic transformation. Examples of traits transferred to inbred maize line NP2222 include, but are not limited to, waxy starch, herbicide tolerance, resistance for bacterial, fungal, or viral disease, insect resistance, enhanced nutritional quality, improved performance in an industrial process, altered reproductive capability, such as male sterility or male fertility, yield stability and yield enhancement. Other traits transferred to inbred maize line NP2222 are for the production of commercially valuable enzymes or metabolites in plants of inbred maize line NP2222.
Traits transferred to maize inbred line NP2222 are naturally occurring maize traits, which are preferably introgressed into inbred maize line NP2222 by breeding methods such as backcrossing, or are heterologous transgenes, which are preferably first introduced into a maize line by genetic transformation using genetic engineering and transformation techniques well known in the art, and then introgressed into inbred line NP2222. Alternatively a heterologous trait is directly introduced into inbred maize line NP2222 by genetic transformation. Heterologous, as used herein, means of different natural origin or represents a non-natural state. For example, if a host cell is transformed with a nucleotide sequence derived from another organism, particularly from another species, that nucleotide sequence is heterologous with respect to that host cell and also with respect to descendants of the host cell which carry that gene. Similarly, heterologous refers to a nucleotide sequence derived from and inserted into the same natural, original cell type, but which is present in a non-natural state, e.g. a different copy number, or under the control of different regulatory sequences. A transforming nucleotide sequence may comprise a heterologous coding sequence, or heterologous regulatory sequences. Alternatively, the transforming nucleotide sequence may be completely heterologous or may comprise any possible combination of heterologous and endogenous nucleic acid sequences.
A transgene introgressed into maize inbred line NP2222 typically comprises a nucleotide sequence whose expression is responsible or contributes to the trait under the control of a promoter appropriate for the expression of the nucleotide sequence at the desired time in the desired tissue or part of the plant. Constitutive or inducible promoters are used. The transgene may also comprise other regulatory elements such as for example translation enhancers or termination signals. In a preferred embodiment, the nucleotide sequence is the coding sequence of a gene and is transcribed and translated into a protein. In another preferred embodiment, the nucleotide sequence encodes an antisense RNA, a sense RNA that is not translated or only partially translated, a t-RNA, a r-RNA or a sn-RNA.
Where more than one trait are introgressed into inbred maize line NP2222, it is preferred that the specific genes are all located at the same genomic locus in the donor, non-recurrent parent, preferably, in the case of transgenes, as part of a single DNA construct integrated into the donor""s genome. Alternatively, if the genes are located at different genomic loci in the donor, non-recurrent parent, backcrossing allows to recover all of the morphological and physiological characteristics of inbred maize line NP2222 in addition to the multiple genes in the resulting maize inbred line.
The genes responsible for a specific, single gene trait are generally inherited is through the nucleus. Known exceptions are, e.g. the genes for male sterility, some of which are inherited cytoplasmically, but still act as single gene traits. In a preferred embodiment, a heterologous transgene to be transferred to maize inbred line NP2222 is integrated into the nuclear genome of the donor, non-recurrent parent. In another preferred embodiment, a heterologous transgene to be transferred to into maize inbred line NP2222 is integrated into the plastid genome of the donor, non-recurrent parent. In a preferred embodiment, a plastid transgene comprises one gene transcribed from a single promoter or two or more genes transcribed from a single promoter.